The two objectives of this research are: (1) to gain better understanding of the structure and function of the small intestinal mucosa in normal man, and (2) to apply this knowledge to studies of the pathogenesis of various small intestinal diseases. A multidisciplinary approach will be used, employing the following disciplines: histology, electron microscopy, biochemistry, bacteriology, virology and gastroenterology. Sufficient quantities of mucosal tissue can be obtained from volunteers and patients under physiological conditions to make such studies possible.